Wave cancellation system for a floating drilling vessel



July 5, 1966 B. L, GOEPFERT ETAL 3,259,371

WAVE CANCELLATION SYSTEM FOR A FLOATING DRILLING VESSEL Filed Sept. 18, 1964 2 Sheets-Sheet l INVENTORS'.

B. L. GOEPFERT H. SHATTO 2. W

THEIR ATTORNEY July 5, 1966 Filed Sept. 18, 1964 B. L. GOEPFERT ETAL WAVE CANCELLATION SYSTEM FOR A FLOATING DRILLING VESSEL AIR SUPPLY AIR TANK HYDRAU LIC CONTROL VA LV E 2 Sheets-Sheet 2 A POSITION 4o 1 TRANSDUCER CONTROLLER n A M i l: E 1

FIG. 2

INVENTORS:

B. L. GOEPFERT H. L. SHATTO THE\R ATTORNEY United States Patent 3,259,371 WAVE CANCELLATION SYSTEM FOR A FLOATING DRILLING VESSEL Benjamin L. Goepfert, West Covina, Calif., and Howard L. Shatto, Jr., Glenville, Conn., assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed Sept. 18, 1964, Ser. No. 397,493

6 Claims. (Cl. 254-173) This invention pertains to floating drilling vessels and more particularly, to a system that is designed to cancel the eifect of vertical motion of the drilling vessel caused by waves and other motion of the water.

In drilling of oil wells and the like from floating vessels, it is necessary to make some provision for vertical motion of the vessel caused by wave act-ion and other forces. The present practice has been to use a splined axially extendable member in the drill string that is commonly referred to as a bumper sub. This permits the vessel to move vertically without causing undue loads or other stresses on the drill string. While this provides a means for canceling the wave action'when actually drilling, it is not satisfactory when it is desired to log the borehole or to use the drill string for the setting of packers and the like or to position objects external to the drill string and well head. When logging the borehole, it is necessary to know the exact position of the downhole logging tool in the borehole in order that the information obtained may be accurately correlated with the depth of the borehole. Likewise, when it is desired to set packers for other equipment, it is necessary to know the exact length of the drill string that extends into the borehole. It is readily appreciated that vertical motion of the drilling vessel will cause either the downhole logging tool or the drill string to oscillate or move in and out of the borehole depending upon the vertical movement of the drilling vessel.

The present practice with regard to logging surveys of boreholes is to use a mechanical system of weights, cables and pulleys to compensate for the vessel movement. These systems usually include a weight on the ocean floor for anchoring one end of a cable with the other end of the cable passing over a sheave or similar device and having a weight suspended at its free end. The anchored cable thus senses the vertical movement of the vessel while the suspended weight is utilized to generate a force that takes in or pays out the logging cable that suspends the logging instrument in the borehole. 'In this manner the logging instrument is maintained at a substantially fixed position in the borehole regardless of the vertical movement of the drilling vessel.

While the above mechanical system is suitable for compensating for wave action when relatively lightweight logging tools are suspended in the borehole, it is of course inadequate for compensating for wave actions when heavy apparatus as for example, a drill string is suspended in the borehole. Of course, it would be theoretically possible to design such a mechanical system to suspend any desired weight in a borehole but such systems would be unwieldy and substantially inoperable. The weights required would be so large that it would be substantially impossible to handle them on a floating drilling vessel.

Accordingly, this invention is directed to a system for compensating for wave action when relatively heavy weights must be suspended in a borehole or externally thereto at a constant depth or must be lowered at a steady rate with respect to the ocean floor rather than with respect to the vessel. The system of this invention utilizes a means that measures the vertical movement of the vessel, and generates a signal proportional thereto. The signal is used to control the position of a linear actuating device that takes in or pays out cable as required to main- 3,259,371 Patented July 5, 1966 tain at a constant position the device suspended below the floating vessel. While various linear positioning devices may be used, a hydraulic cylinder is preferred since the position of the cylinder may be easily controlled by means of a servo valve. The servo valve in turn can be positioned by means of an electrical signal which is derived from the device that measures the vertical movement at the vessel.-

The above advantages of this invention will be more easily understood from the following detailed description when taken in conjunction with the attached drawings in which:

FIGURE 1 is an elevational view of the floating drilling vessel showing one embodiment of this invention; and,

FIGURE 2 is an elevation view of a second drilling vessel showing a second emobodiment of this invention having a control system incorporated therein.

Referring now to FIGURE 1 there is shown a drilling vessel 10 floating on a body of water 11. The drilling vessel may be maintained in position by various devices, for example, a series of anchors 8 and mooring lines 9. The drilling vessel is provided with a derrick 12 and draw works 13. Derrick and draw works are conventional rotary drilling equipment that is used in fixed drilling positions and on floating drilling vessels. The draw works supports a drill string 14 which extends downwardly through an opening 7 in the floating vessel 10 to the wellhead 15. The wellhead 15 is positioned on the ocean floor 16 and contains the necessary equipment for controlling the W611 and permitting re-entry of the drill string 14 after it has been withdrawn from the well. All of the above items are conventional equipment Well known to those skilled in the art of offshore drilling from floating vessels and thus will not be described in greater detail.

A remotely controlled manipulator or inspecting device 20 is shown suspended below the floating vessel 10 adjacent to the drill string 14. The device 20 may be a mechanical operator designed to operate or perform other functions on the wellhead 15. It is normally desired that the operator 20 be positioned adjacent to the wellhead 15 and maintained in a relatively fixed position thereto in order that it may perform the desired operations on the wellhead 1 5. At times it may be possible to land the manipulator 20 on a fixed platform projecting from the wellhead 15 and then maintained suflicient slack in the supporting cable 21 to permit the manipulator to rest on the platform. Although the manipulator 20 rests on a flxed platform, it is still required that it be lowered gently into contact wit-h the projecting platform to prevent physical damage. As the manipulator 20 approaches the landing platform it is of course necessary to maintain it 1 in a relatively flxed position with respect to the landing platform regardless of the vertical motion of the floating vessel 10. Any unwanted vertical movement of the manipulator 20 could cause the manipulator to strike the landing platform or the ocean bottom '16 with sufficient force to damage it.

To maintain the manipulator 20 in a relatively fixed position regardless of the vertical movement of the floating vessel 10, the present invention utilizes a movable sheave 23 over which the cable 21 passes. The cable 21 is used to raise and lower the manipulator 20 and is anchored on a winch 22. The movable sheave 23 is moved along the vertical axis an amount equal and opposite to the vertical movement with respect to the ocean floor of the floating vessel 10. The movable sheave 23 is suspended by means of a cable 24 which is anchored to a drum 25. The vertical motion of the floating vessel 10 is determined by means of a line 36 that is anchored at its lower end to a weight 37 resting on the floor of the ocean 16. The

other end of the line 36 is anchored to the drum 25. Also secured to the drum 25 is a line 30 whose opposite end is secured to the movable member of the linear positioning device 31.

The linear positioning device 31 is preferably a device which maintains a constant tension or force on the line 30 of suflicient magnitude to support the suspended string or inspection device and with suflicient excess to hold line 36 taut but not large enough to pick up weight 37 from the ocean floor. A constant tension may be provided by means of a hydraulic cylinder which is supplied with pressurized fluid from a constant pressuresource. For example, the fluid may be supplied from a compressed air bank that is maintained under constant pressure by means of a compressor or the like. The constant pressure source 32 is coupled to one end of the hydraulic cylinder 31 by means of a conduit 33 while the opposite end is exhausted through an Opening 34. The tension force supplied by the device 31 can be varied by changing the average pressure of the air bank 32, thus the required tension can be supplied by the device 31.

When the above system is operated, any vertical motion of the vessel will tend to cause the line 36 to either go slack or to rotate the drum 25. For example, if the vessel 10 rises, the tension in line 36 will tend to increase thus exceeding the present constant tension in device 31 which will cause the drum to rotate in a direction to pay out the cable 24 thus lowering the movable sheave 23. Since the drum has a constant diameter the length of cable 24 that is paid out by the drum will exactly equal the length of the line 36 that is paid out from the drum. Of course, as the drum is rotated by means of the line 36 it will tend to take in the line and thus cause the hydraulic cylinder to work against the constant pressure source 32. Thus, it is necessary that the weight 37 be of sufficient size to generate a force that exceeds the force generated by the combination of the hydraulic cylinder and constant pressure source less the weight suspended from cable 21. It should be noted that winch 22 is placed a considerable distance from the sheave 23 to minimize the angular movement of the line from the winch to the sheave 23.

In case the vessel falls, the opposite operation of that described above will take place. More particularly, the cable 36 will tend to go slack and the linear positioning device 31 will remove the line 30 from the drum 2.5. This will rotate the drum 25 in a direction so as to take in both the cable 24 and the line 36. Thus the slack will be removed from the line 36 and the cable 24 will be taken in an amount equal to the downward movement of the vessel 10. Thus, regardless of the vertical movement of the vessel 10, the operator 20 will be maintained in an essentially fixed vertical position.

Referring now to FIGURE 2 there is shown a second embodiment of this invention wherein a floating vessel 40 is maintained in a desired position by means of the anchor and the mooring line 9 as shown in FIGURE 1. The vessel 40 is also provided with a drilling derrick 41 and a draw works 42 having a traveling block 43. The draw works is used for raising and lowering a drill pipe 44 in the borehole whose top is closed by means of the wellhead 45. As explained above all of the drill rig is conventional equipment well known to those skilled in the art.

The system shown in FIGURE 2 is designed ot maintain the drill string 44 in a constant fixed vertical position regardless of the vertical motion of the floating drilling vessel 40. To accomplish this the free end of the cable that is used for raising and lowering the traveling block 43 is connected to the movable member of the linear positioning device 51. As explained above with respect to FIGURE 1 the linear positioning or actuating device 51 may take various forms but is preferably a hydraulic type of device capable of generating considerable force. The hydraulic actuator 51 is coupled to a source of constant pressure fluid by means of a conduit 52. A

4 source of constant pressure fluid may take the form of a compressed air bank 53 that is supplied With compressed air through an inlet 54.

The opposite end of the actuator 51 is coupled by means of a conduit to a hydraulic control valve 51. Of course the pneumatic and hydraulic ends of the actuator 51 must be isolated or two actuators in tandem could be used. The hydraulic control valve 61 may be of any well known design such as a servo valve that accepts an electrical signal and then positions hydraulic actuator 51 in proportion to the magnitude of the electrical signal. A suitable valve would be a control valve known as a Moog control valve.

The hydraulic control valve 61 receives a source of pressurized hydraulic fluid through a conduit 62 from a pump 65. The pump 65 takes a suction from a sump or reservoir 64 to which the control valve 61 discharges through a conduit 63.

The vertical position of the floating vessel 40 is determined by means of a line 71 whose lower end is anchored by a weight or other anchoring device 72 to the ocean floor 16. The opposite end of the line 71 is maintained on a winch that is provided with a constant tensioning drive means. The winch 70 is provided with a constant tensioning drive to insure that the line 71 is paid out as the vessel 40 rises and is taken in as the vessel 40 falls. The amount of line paid out from the winch 7t) and thus the vertical position of the floating vessel 40 is determined by means of a position transducer 66. The position transducer is coupled to the winch by means of a mechanical drive means shown schematically at 73. A suitable positioning transducer would by a synchro transmitter that is driven by the winch and thus provides an electrical signal which is related to the length of the line 71. The electrical signal from the position transducer 66 is supplied to a controller 67. The controller 67 can be a normal process type controller that is provided with a fixed set point in addition to reset and proportional actions. A rod position detecting device 68 is mounted on the actuator 51 to detect the position of the actuator rod and supply a related electrical signal to the controller 67 by means of lead 69. Thus the controller will compare the signal from the position transducers 66 with a set point and supply and difference as an error or correcting signal to the hydraulic control valve 61. The hydraulic control valve in turn will admit or exhaust hydraulic fluid from one end of the actuator 51, thus taking in or paying out the line 50 to maintain the drill string at a constant vertical position.

When this system shown in FIGURE 2 is operated the vertical movement of the floating vessel 40 is measured by the position transducer 66. The signal from the position transducer will be supplied to the controller 67 that will position the hydraulic control valve 61 in relation to the error signal. The hydraulic control valve 61 will then position the hydraulic actuator 51 to either take in or pay out the cable 50 to maintain the drill string 44 at a constant vertical position. The rod position detecting device 68 will supply a feedback signal to the controller and thus stabilize the system. When it is desired to pull the drill string from the borehole the hydraulic actuator 51 can be locked in a fixed position which will have the same eifect as anchoring the end of the cable 50. With one end of the cable anchored the draw works 42 can then operate in its normal manner to pull the drill string from the borehole.

While the hydraulic actuator 51 is shown as utilizing hydraulic pressure to move it in one direction against a constant pressure generated by the air bank 53, other types of actuators could also be used. For example, a double acting hydraulic actuator in which the control valve 61 admits fluid to one end of the cylinder while it exhausts from the other end to reposition the actuator could be used. Also, the hydraulic actuator 51 could be a single ended actuator while the constant pressure being supplied by a separate actuator. The arrangement of two separate actuators would be desirable where it is necessary to vary the size of the actuators to insure that they generate the required force to overcome the etfects of vertical motion of the vessel. With separate actuators, it is a simple matter to vary the diameter of the actuators and thus control the amount of force generated by each actuator.

For example, in FIGURE 2 which is adaptable to heavier loads, the major premise is the use of an air (compressible gas) to supply from 90% to 110% of the force required to balance the system. The hydraulic system power requirement is therefore reduced to say of the total and can alternately compress the gas in the receiver and cause it to expand as the vessel rises and falls. That is-the air receiver merely serves as a bias to the load. This efiects a saving in horsepower requirements in the hydraulic system.

We claim as our invention:

1. An apparatus for supporting a device from a floating marine platform that moves vertically in response to wave action, said apparatus comprising:

an elongated member extending from said platform to said device for supporting said device;

measuring means disposed on said platform to measure the vertical movement of the platform relative to the bottom of the water;

an actuating means disposed on the platform and coupled to the elongated member for moving said elongated member to take in or pay out the member as the platform moves in response to wave action; and

said actuating means having a linearly movable member, said linearly movable member being coupled to said measuring means to position said actuating means in response to the movement of said platform relative to the bottom of the Water supporting the platform.

2. The apparatus of claim 1 in which the actuating means comprises a linear actuator supplied with energy from an external source.

3. The apparatus of claim 2 in which said measured vertical motion is used to control the amount of energy supplied to the actuating means.

4. The apparatus of claim 1 in which said actuating means comprises:

a double acting actuator;

a receiver containing a compressible gas;

a source of fluid pressure; and

said receiver being coupled to said actuator to move said actuator in one direction to substantially balance the load created by the weight of the device and said source of fluid pressure being coupled to said actuator to move said actuator in the other direction to compensate for the vertical motion of the platform.

5. An apparatus for supporting a device from a floating marine platform that moves vertically in response to wave action, said apparatus comprising:

a hoist means extending from the platform to the device for supporting said device;

a fluid pressure actuated linear positioning means, said linear positioning means being coupled to said hoist means and having separate chambers for moving the device in opposite directions;

a source of constant pressure fluid, said constant pressure source being coupled to one chamber of said linear positioning means to move said device in one direction, the pressure of said fluid and the size of said chamber being controlled to cause said linear positioning means in cooperation with said hoist means to supply a force tending to lift the device equal to at least percent of the weight of the device;

measuring means disposed on the platform to measure the vertical movement of the platform relative to the bottom of the water and supply a related electrical signal;

a control means, said measuring means being coupled to said control means;

a source of pressurized fluid;

a servo valve, said source of pressurized fluid being coupled to said servo valve, said servo valve being coupled to the other chamber of the linear positioning means;

said control means being coupled to said servo valve to vary the position thereof in response to the vertical movement of the platform.

6. The apparatus of claim 5 and in addition,

a position transducer, said transducer being disposed to measure the position of the linear positioning means, said transducer in addition being coupled to said control means to provide a feedback signal.

References Cited by the Examiner UNITED STATES PATENTS 3,088,710 5/1963 Evans 254172 3,158,206 11/ 1964 Kammerer 5 3,189,196 6/1965 Carl et al. 254-173 3,204,708 9/1965 Berne 175---6 3,208,728 9/1965 Parks 254-172 EVON C. BLUNK, Primary Examiner.

A. H. NIELSEN, Assistant Examiner. 

1. AN APPARATUS FOR SUPPORTING A DEVICE FOR A FLOATING MARINE PLATFORM THAT MOVES VERTICALLY IN RESPONSE TO WAVE ACTION, SAID APPARATUS COMPRISING: AN ELONGATED MEMBER EXTENDING FROM SAID PLATFORM TO SAID DEVICE FOR SUPPORTING SAID DEVICE; MEASURING MEANS DISPOSED ON SAID PLATFORM TO MEASURE THE VERTICAL MOVEMENT OF THE PLATFORM RELATIVE TO THE BOTTOM OF THE WATER; AN ACTUATING MEANS DISPOSED ON THE PLATFORM AND COUPLED TO THE ELONGATED MEMBER FOR MOVING SAID ELONGATED MEMBER TO TAKE IN OR PAY OUT THE MEMBER AS THE PLATFORM MOVES IN RESPONSE TO WAVE ACTION; AND SAID ACTUATING MEANS HAVING A LINEARLY MOVABLE MEMBER, SAID LINEARLY MOVABLE MEMBER BEING COUPLED TO SAID MEASURING MEANS TO POSITION SAID ACTUATING MEANS IN RESPONSE TO THE MOVEMENT OF SAID PLATFORM RELATIVE TO THE BOTTOM OF THE WATER SUPPORTING THE PLATFORM. 